Most current videoconferencing systems have shared resources in conference rooms to allow room-to-room video communication among groups of people. Recently, however desktop videoconferencing systems have emerged as an alternative. These desktop systems allow people to communicate with video calls on an individual basis, and are typically implemented on personal computers (PC's) that can also be used to run other applications, such as word processing or spreadsheets.
Many current desktop systems are interconnected through an integrated services digital network (ISDN) with basic rate interface (BRI) lines. A BRI line has two independent B-channels, each of which can carry data at rates of about 64 kb/sec; and a D-channel, which carries signaling information, such as a called directory number, a calling directory number, and the rate of the call. A caller's directory number, which is given by a telephone service provider, is also called an automatic number identification (ANI).
A videoconferencing calling station, such as a PC-based desktop system, includes at least a microphone and a camera for picking up voice and video signals, and a speaker and a monitor for transmitting voice and video signals. To improve the quality of these transmissions by increasing the bandwidth, the voice and video signals are split up and are transmitted over the two separate B-channels with two telephone calls. The caller enters two telephone numbers to initiate two calls, which are routed through different paths in the ISDN to a receiving station. The receiving station receives signals over the two B-channels, combines them, and provides the video signals on the monitor and voice signals over the speaker.
Because there are two channels and two calls, each calling station has one or two ANI's associated with it (and not with any other calling station). These two ANI's may be the same number or different numbers for each channel, depending primarily on how the telephone system and switching network are configured by the telephone service provider.
One application for desktop videoconferencing technology is for customer service. Customers needing service make video calls to agents in a customer service office. The calls are delivered from a customer's calling station over BRI lines to the ISDN, which switches the calls to the service providing company over a primary rate interface (PRI) line. A PRI line has a D-channel to carry signaling information, and has a relatively large number of B-channels compared to a BRI line.
At the customer service office, a resident access switch receives the calls over the PRI line and switches them over BRI lines to the customer service agents, each of whom has a receiving station, preferably implemented as a PC-based desktop system. On the incoming side, the access switch demultiplexes calls that are routed over individual BRI lines to the agents, and on the outgoing side, the access switch multiplexes calls from the agents to the PRI line. The PRI line thus serves as a trunk between the access switch and the ISDN. The access switch has port interfaces to the BRI lines to implement network protocols such that the access switch is transparent to the parties, i.e., the desktop systems appear to be connected directly to the telephone network.
The access switch receives calls based on a called directory number (CDN) and associates calls with this CDN to one of a number of separate receiving stations. The access switch can receive calls with a number of different CDN's and route them to different corresponding groups of receiving stations. To route the calls, the access switch uses a hunting process to find a receiving station having a free B-channel, and routes the call to the interface associated with that receiving station. This conventional hunting process can work in one of several different ways; e.g., it can be based on the longest idle agent or based on a set queue in which stations are taken in order. In a system in which two calls are transmitted, the calls are paired and routed to an agent in the order received.
Such hunting processes may not always work in a customer service application in which multiple calls are provided, however, especially as the use of desktop videoconferencing grows. If two calls are initiated from each of two different calling stations at about the same time, four calls are routed over different paths of the ISDN. If the calls arrive at the access switch such that a first call from the first calling station is followed by a first call from the second calling station, followed by the respective second calls, both first calls would be routed to a first agent, and after these calls are connected, both second calls would be routed to a second agent. Consequently, each party would receive incomprehensible video and voice information.